Various medical procedures require the use of a catheter that has at least two separate fluid flow paths or lumens. Catheters having multiple lumens are important because they reduce the number of tubes that must be placed through a patient's skin. One example of the use of a multiple-lumen catheter is in the extracorporeal treatment of blood, as in hemodialysis. During hemodialysis, two separate paths are necessary for the flow of blood. Specifically, one lumen accommodates blood flow from the patient for the treatment of the blood to remove various toxins. The other lumen accommodates the return flow of treated blood to the patient. A further example of the use of a multiple-lumen catheter is the delivery of incompatible medications and/or intravenous fluids.
Several multiple-lumen catheters are known for these purposes. One example of a hemodialysis catheter is shown in U.S. Pat. No. 4,808,155 (the '155 patent) issued to Mahurkar. The catheter shown in the '155 patent has two separate ports, i.e., an infusion port and a withdrawal port, opening from an infusion lumen and a withdrawal lumen. As shown in the '155 patent, the infusion lumen extends the entire length of the catheter and terminates at a flat distal end. The withdrawal lumen is substantially shorter than the infusion lumen and terminates at a point proximal to the distal end of the catheter. As explained in the '155 patent, the separation of the withdrawal port and the infusion port generally prevents mixing of untreated blood initially drawn into the catheter with treated blood being returned to the patient.
However, several disadvantages result from the placement of the infusion port on the distal end of the catheter as shown in the '155 patent. First, the ports may be partially or totally occluded by a buildup of blood components (fibrin) or when the ports press up against the vessel wall. This situation drastically reduces the effectiveness of the treatment. Second, as fluid exits from the infusion port, the catheter is subject to whipping (a quick back and forth movement inside the vein of a patient). Because whipping causes the catheter to continually batter the inside wall of the vein, the vein will be damaged. In addition, whipping may cause clots to form around the outside surface of the catheter tip. These clots can obstruct blood flow through the vessel. They may also become dislodged, creating a free-floating thrombus in the circulatory system. These fibrin deposits are generated by the endothelium of the vessel wall as an inflammatory reaction to the irritation of the catheter whipping. Clot formation and stricture of blood vessels are common complications associated with the implantation of these catheters. Accordingly, there exists a need for a catheter capable of overcoming the above-referenced problems while avoiding the mixing of fluids from the two lumens.